This invention relates to connection devices for cables having electromagnetic interference (hereinafter EMI) shields and, in particular, connection devices which are used to connect EMI shielded cables without the loss of EMI shielding effectiveness to an EMI enclosure.
As the need for EMI shielded cable has increased, better methods and devices for terminating such shields have been sought. It is generally required to terminate the EMI shield of such cable so that the cable may be connected to bulkheads, control panels, or other EMI enclosures.
An effective shield connection device provides a low impedance path to minimize the amount of electrical coupling and to increase overall EMI shielding efficiency. Particularly, the EMI captured by the EMI shield of the cable is drained through the connection device to ground via a low impedance path. The device generally prevents radiated EMI from entering the shield termination area. The device also confines any EMI energy from radiating from the EMI enclosure to the outside world.
Various methods and devices for terminating EMI shielded cable to solve the above-mentioned problems have been attempted. These methods and devices have included terminating individual cable shielded by attaching a simple ground lead wire to each shield and connecting the ground leads to the rear of a connector or other grounding point. This technique is known as "pigtailing." A more advanced device and technique for pigtailing involves self-pigtailing as discussed in Schwartz, U.S. Pat. No. 3,465,092, wherein a cylindrical, externally threaded element with a plurality of spaced longtitudinal slots is combined with the driving ring which is in threaded engagement with the cylindrical element. The driving ring rotates while carrying a contact annulus provided with a plurality of contact sections. Each contact section extends into a slot. Rotation of the ring moves the annulus and the contact section toward the end of the slot to position and hold leads of shielding.
It has been found that devices using this pigtailing technique have certain shortcomings. Among the shortcomings are that the devices are difficult to assemble and install. Additionally, known devices are typically bulky, inflexible and heavy. Such devices do not provide a block to radiated EMI which can travel parallel to the axis of the cables. It has been known for some time that the axial interstices between the individual shields can provide a window through which radiated EMI energy may travel.
Ellis, et al, U.S. Pat. No. 3,541,495 discloses a coaxial contact for terminating both the center conductor and the braid shield of a coaxial cable with soldered connections. Ellis, et al, includes outer contact which is provided with a window to permit radiant heat energy to be directed onto an internal sleeve and solder insert. A second heat-recoverable sleeve and solder insert are positioned around the outside of an outer contact with the solder insert located over a second window. When the cable is inserted into the contact, the center conductor is located under the first window and the braid is beneath the second window. Recovery of the external sleeve causes solder to be forced through the second window to make a soldered connection between the braid and the inside of the outer contact which is insulated from the inner contact.
The invention disclosed herein is a device for connecting the shield of one or more EMI shielded cables to an EMI enclosure. The device includes an electrically conductive body defining a shield termination enclosure, having a plurality of openings, extending from one end of the body to the other and located generally parallel to the longitudinal axis of the body. The body includes a means for accessing the opening. The device includes a means for applying fixable electrically conductive material to connect one or more cable EMI shields to the body. Sufficient conductive material is provided to fill the opening of the body, thereby, blocking possible EMI windows.